Space manufacturing


Space manufacturing or In-space manufacturing is the fabrication, assembly or integration of tangible goods beyond Earth's atmosphere, involving the transformation of raw or recycled materials into components, products, or infrastructure in space, where the manufacturing process is executed either by humans or automated systems by taking advantage of the unique characteristics of space. Synonyms of Space/In-space manufacturing are In-orbit manufacturing, Off-Earth manufacturing, Space-based manufacturing, Orbital manufacturing, In-situ manufacturing, In-space fabrication, In-space production, etc. In-space manufacturing is a part of the broader activity of in-space servicing, assembly and manufacturing and is related to in situ resource utilization.
Three major domains of In-space manufacturing are ISM for space where products remain in space, ISM for Earth where goods with improved properties produced in outer-space microgravity are transported back to Earth, and ISM for surface where goods are produced on or sent to surfaces of celestial bodies like the Moon, Mars, and asteroids.
In-space manufacturing uses processes such as additive manufacturing, subtractive manufacturing, hybrid manufacturing and welding.
In-space manufacturing removes spacecraft design limitations due to launch parameters and volume limitations imposed by payload size. It allows for recycling of launched materials, utilization space-mined resources and on-demand spare parts production, which enables on-site repair of critical parts and infrastructure development. It takes advantage of unique space features such as microgravity, ultra-vacuum and containerless processing, which are difficult to do on Earth.

Areas

In-space manufacturing can be categorized into three different areas according to the end use of manufactured products. In-space manufacturing for space involves activities focused on in-orbit construction intended for use in space. ISM for Earth is the production of new materials and products that exhibit enhanced properties when manufactured in microgravity, subsequently transported back to Earth. Lastly, ISM for surface extends to surface operations on celestial bodies such as the Moon, Mars, and asteroids.

Rationale

There are several motivating factors behind in-space manufacturing. The space environment, in particular the effects of microgravity and vacuum, enable the research of and production of goods that could otherwise not be manufactured on Earth. Secondly, the extraction and processing of raw materials from other astronomical bodies, also called In-Situ Resource Utilisation, could enable more sustainable space exploration missions at reduced cost compared to launching all required resources from Earth. Furthermore, raw materials could be transported to low Earth orbit where they could be processed into goods that are shipped to Earth. By replacing terrestrial production on Earth, this seeks to preserve the Earth. Moreover, raw materials of very high value, for example gold, silver, or platinum, could be transported to low Earth orbit for processing or transfer to Earth which is thought to have the potential to become economically viable. In-space manufacturing supports long-duration space missions and colonization by enabling on-site repair and infrastructure development beyond Earth. Additionally, in the area of spaceflight technology, space manufacturing enhances mission safety by decentralizing manufacturing activities and establishing redundancy in critical systems, allows for customized production tailored to specific mission requirements, fostering rapid iteration and adaptation of designs, drives technological innovation in materials science, robotics, and additive manufacturing, with applications extending beyond space exploration, and lays the foundation for space-based infrastructure development, supporting a wide range of commercial activities and scientific research.

History

During the Soyuz 6 mission of 1969, Russian cosmonauts performed the first welding experiments in space. Three different welding processes were tested using a hardware unit called Vulkan. The tests included welding aluminum, titanium, and stainless steel.
The Skylab mission, launched in May 1973, served as a laboratory to perform various space manufacturing experiments. The station was equipped with a materials processing facility that included a multi-purpose electric furnace, a crystal growth chamber, and an electron beam gun. Among the experiments to be performed was research on molten metal processing; photographing the behavior of ignited materials in zero-gravity; crystal growth; processing of immiscible alloys; brazing of stainless steel tubes, electron beam welding, and the formation of spheres from molten metal. The crew spent a total of 32 man-hours on materials science and space manufacturing investigation during the mission.
The Space Studies Institute began hosting a bi-annual Space Manufacturing Conference in 1977.
Microgravity research in materials processing continued in 1983 using the Spacelab facility. This module has been carried into orbit 26 times aboard the Space Shuttle,. In this role the shuttle served as an interim, short-duration research platform before the completion of the International Space Station.
In February 1994 and September 1995, the Wake Shield Facility was carried into orbit by the Space Shuttle. This demonstration platform used the vacuum created in the orbital wake to manufacture thin films of gallium arsenide and aluminum gallium arsenide.
On May 31, 2005, the recoverable, uncrewed Foton-M2 laboratory was launched into orbit. Among the experiments were crystal growth and the behavior of molten-metal in weightlessness.
The completion of the International Space Station has provided expanded and improved facilities for performing industrial research. These have and will continue to lead to improvements in our knowledge of materials sciences, new manufacturing techniques on Earth, and potentially some important discoveries in space manufacturing methods. NASA and Tethers Unlimited will test the Refabricator aboard the ISS, which is intended to recycle plastic for use in space additive manufacturing.
The Material Science Laboratory Electromagnetic Levitator on board the Columbus Laboratory is a science facility that can be used to study the melting and solidification properties of various materials. The Fluid Science Laboratory is used to study the behavior of liquids in microgravity.

Material properties in the space environment

There are several unique differences between the properties of materials in space compared to the same materials on the Earth. These differences can be exploited to produce unique or improved manufacturing techniques.
  • The microgravity environment allows control of convection in liquids or gasses, and the elimination of sedimentation. Diffusion becomes the primary means of material mixing, allowing otherwise immiscible materials to be intermixed.
  • The environment allows enhanced growth of larger, higher-quality crystals in solution.
  • The ultraclean vacuum of space allows the creation of very pure materials and objects. The use of vapor deposition can be used to build up materials layer by layer, free from defects.
  • Surface tension causes liquids in microgravity to form perfectly round spheres. This can cause problems when trying to pump liquids through a conduit, but it is very useful when perfect spheres of consistent size are needed for an application.
  • Space can provide readily available extremes of heat and cold. Sunlight can be focused to concentrate enough heat to melt the materials, while objects kept in perpetual shade are exposed to temperatures close to absolute zero. The temperature gradient can be exploited to produce strong, glassy materials.

    Material processing

For most manufacturing applications, specific material requirements must be satisfied. Mineral ores need to be refined to extract specific metals, and volatile organic compounds will need to be purified. Ideally these raw materials are delivered to the processing site in an economical manner, where time to arrival, propulsion energy expenditure, and extraction costs are factored into the planning process. Minerals can be obtained from asteroids, the lunar surface, or a planetary body. Volatiles could potentially be obtained from a comet, carbonaceous chondrite or "C-Type" asteroids, or the moons of Mars or other planets. It may also prove possible to extract hydrogen in the form of water ice or hydrated minerals from cold traps on the poles of the Moon.
Unless the materials processing and the manufacturing sites are co-located with the resource extraction facilities, the raw materials would need to be moved about the Solar System. There are several proposed means of providing propulsion for this material, including solar sails, electric sails, magnetic sails, electric ion thrusters, microwave electrothermal thrusters, or mass drivers.
At the materials processing facility, the incoming materials will need to be captured by some means. Maneuvering rockets attached to the load can park the content in a matching orbit. Alternatively, if the load is moving at a low delta-v relative to the destination, then it can be captured by means of a mass catcher. This could consist of a large, flexible net or inflatable structure that would transfer the momentum of the mass to the larger facility. Once in place, the materials can be moved into place by mechanical means or by means of small thrusters.
Materials can be used for manufacturing either in their raw form, or by processing them to extract the constituent elements. Processing techniques include various chemical, thermal, electrolytic, and magnetic methods for separation. In the near term, relatively straightforward methods can be used to extract aluminum, iron, oxygen, and silicon from lunar and asteroidal sources. Less concentrated elements will likely require more advanced processing facilities, which may have to wait until a space manufacturing infrastructure is fully developed.
Some of the chemical processes will require a source of hydrogen for the production of water and acid mixtures. Hydrogen gas can also be used to extract oxygen from the lunar regolith, although the process is not very efficient. So a readily available source of useful volatiles is a positive factor in the development of space manufacturing. Alternatively, oxygen can be liberated from the lunar regolith without reusing any imported materials by heating the regolith to in a vacuum. This was tested on Earth with lunar simulant in a vacuum chamber. As much as 20% of the sample was released as free oxygen. Eric Cardiff calls the remainder slag. This process is highly efficient in terms of imported materials used up per batch, but is not the most efficient process in energy per kilogram of oxygen.
One proposed method of purifying asteroid materials is through the use of carbon monoxide. Heating the material to and exposing it to CO causes the metals to form gaseous carbonyls. This vapor can then be distilled to separate out the metal components, and the CO can then be recovered by another heating cycle. Thus an automated ship can scrape up loose surface materials
from, say, the relatively nearby 4660 Nereus, process the ore using solar heating and CO, and eventually return with a load of almost pure metal. The economics of this process can potentially allow the material to be extracted at one-twentieth the cost of launching from Earth, but it would require a two-year round trip to return any mined ore.